In rubber and plastic processing technology, in order to obtain a mixture suitable for transformation into a finished or semi-finished product, use can be made of a mixing machine of the so-called internal mixer type, having a mixing chamber inside which two shaped rotors rotate about parallel axes so as to achieve microdispersion and homogenization of the various components of the batch being processed throughout its mass.
The material to be mixed is fed into the chamber via openings arranged on the sides of the machine in an elevated position with respect to the mixing chamber and leading into the latter via a duct arranged parallel to the vertical axis of the machine.
Once the material has been fed, it is kept pressed inside the chamber by means of a presser element which can be actuated in a direction parallel to the vertical axis of the machine and in both the raising direction and lowering direction so as to allow respectively opening and closing of the hatch of the opening for loading the material and compression of the latter during processing.
A choice for actuating the presser element is illustrated, for example, in with at least two hydraulic cylinders installed laterally with respect to the material loading well.
This mixer, however, has the drawback that hydraulic cylinders are connected to the bottom part of the machine structure to avoid increasing the vertical dimensions of the machine itself. Therefore, in the case of actuation by means of a single pair of cylinders, the latter must be symmetrically arranged along a diagonal of the quadrilateral, the vertices of which are formed by the guides of a cross-member connected to the top end of the support rod of the presser element. With this arrangement, which cannot be avoided since otherwise it would cause blocking of the lateral openings for feeding of the chemical components, it is difficult to obtain correct balancing of the cylinder action.
In addition, the actuating rod of the presser element is rigidly fixed to two upper and lower guides elements. Hence, the transverse forces generated by the mixing thrust are directly transmitted to the rod which, owing to the rigid connections, may undergo deformation preventing correct sliding thereof.